Apparatus for an internal combustion engine

ABSTRACT

An apparatus for achieving internal EGR in a four-stroke internal combustion engine which, for each cylinder, has at least one inlet valve and at least one exhaust valve for controlling the connection between combustion chambers in the cylinder and an inlet system and exhaust system respectively. A rotary camshaft with a cam curve is designed to interact with a follower member and has a first lobe portion for generating the normal exhaust valve lift of the engine. The camshaft is provided with a second lobe portion, which has a height measurement over and above its basic curve which falls short of the measurement for normal exhaust valve clearance when driving at low load and accompanying low heat development in the engine. As a result of thermal expansion in the valve mechanism, the height measurement exceeds the measurement for normal exhaust valve clearance when driving at high load and accompanying high heat development in the engine. The second lobe portion is situated within a crankshaft angular range of about 360-480 degrees.

BACKGROUND AND SUMMARY

The present invention relates to an apparatus for achieving internal EGRin a four-stroke internal combustion engine.

Exhaust gas recirculation, so-called EGR, is a widely known method inwhich some of the total exhaust flow of the engine is recirculated formixing with incoming air to the cylinders of the engine. It therebybecomes possible to reduce the quantity of nitrogen oxide in the exhaustgases.

This recirculation is usually effected via shunt valves and linesextending on the outside of the engine, from the exhaust side to theinlet side. In certain cases, it is desirable for spatial reasons to beable to achieve EGR-mixing without such arrangements. To this end, ithas been proposed to achieve EGR-mixing by utilizing the usual inlet andoutlet valves of the engine for the return flow of exhaust gases fromthe exhaust manifold of the engine to the cylinders, so-called internalEGR (IEGR). This return flow is achieved by an extra opening of theexhaust valve during the working cycle of the engine.

There are pressure surges on the exhaust side which are higher than thecylinder pressure. If the exhaust valve is opened under such a pressurepeak, exhaust gases flow backward into the cylinder.

It is known, for example through WO 03/031778, to make use of atwo-level valve clearance, for example a mechanically adjusted valveclearance combined with a hydraulically adjusted O-clearance which canbe activated/deactivated depending on the operating situation of theengine, for example changing between positive engine power and enginebraking (decompression brake) respectively. The extra valve motion whichis then activated/deactivated can in this case be hidden beneath themechanically adjusted valve clearance, but emerges when O-clearance isactivated. This method can also be used to activate/deactivate an extravalve motion in order to obtain internal EGR.

WO 03/067067 describes a different valve mechanism having an activablesecondary rocker arm which can utilize the usual cam lobe to produceextra valve lift for internal EGR.

With the mechanisms described above, it is therefore possible toactivate the internal EGR function, which gives an EGR levelpredetermined by cam lobe and rocker arm geometry. Usually, the EGRfunction is optimized for a high r.p.m. range within which the engine isexpected to operate. When the engine operates within a lower r.p.m.range, the EGR quantity can become too high, leading to increased fuelconsumption and more smoke in the exhaust gases. If this EGR function isnot active within this r.p.m. range, the nitrogen oxide emissionsincrease. It is desirable to be able to obtain lower internal EGR atlower engine speeds.

It is desirable to produce a valve system which allows changing betweenvarious EGR levels.

According to an aspect of the present invention, an apparatus forachieving internal EGR in a four-stroke internal combustion engineincludes, for each cylinder and piston associated with the cylinder atleast one inlet valve and at least one exhaust valve for controllingconnection between a combustion chamber in the cylinder and an inletsystem and exhaust system respectively. The apparatus also includes, foreach cylinder and piston associated with the cylinder, a rotary camshaftwith a cam curve designed to interact with a follower member. The camcurve has a first lobe portion for generating a normal exhaust valvelift of the engine and a second lobe portion having a height measurementover and above a basic curve of the camshaft. The height measurement forthe second lobe portion falls short of a height measurement for normalexhaust valve clearance when driving at a first load and heatdevelopment in the engine, and which height measurement for the secondlobe portion, as a result of thermal expansion in the valve mechanism,exceeds the measurement for normal exhaust valve clearance when drivingat a second load and heat development in the engine, the second load andheat development being higher than the first load and heat development.The second lobe portion is situated within a crankshaft angular range ofabout 360-480 degrees.

BRIEF DESCRIPTION OF FIGURES

The invention will be described in greater detail below with referenceto illustrative embodiments shown in the appended drawings, in which:

FIG. 1 shows a valve mechanism with a facility for changing betweenvarious operating modes according to the invention, and

FIG. 2 shows a typical lifting curve for maneuvering of the valvemechanism according to FIG. 1.

DETAILED DESCRIPTION—

The invention will be described below in connection with a valvemechanism which is described in greater detail in PCT/SE03/01630.

The valve mechanism shown in FIG. 1 is placed on a cylinder head andcomprises exhaust valves 10 with valve springs 11 and a common valveyoke 12. The yoke is acted upon by a rocker arm 13, which is mountedpivotably about a rocker arm shaft 14. The rocker arm 13 has on one sideof the shaft 14 a valve pusher arm 15 and on the other side a camfollower arm 16, which is provided with a first follower member in theform of a rocker arm roller 17, which normally interacts with a camshaft18. In addition, the cam follower arm 16 is provided with a secondaryarm 19, which is mounted pivotably on the outer end 16 a of the arm andis provided with a second follower member in the form of a finger 20.

The secondary arm 19 is switchable between an inactive and an activeposition by means of a hydraulic piston 21 placed in the rocker arm.This is coupled to the secondary arm 19 in a substantially play-freemanner by a fork 19 a.

In the inactive position (not shown in FIG. 1), the rocker arm 13 isacted upon by the cam lobe 22 of the camshaft 18 only via the rocker armroller 17. In the active position (as shown in FIG. 1), the rocker arm13 is acted upon by the cam ridge 22 of the camshaft, additionally viathe finger 20. The geometry of the secondary arm 19 is tailored so thatthe rocker arm, in the active position, is activated by the cam lobe 22at the desired phase angle, in this case with a delay of about 80-110degrees in the direction of rotation of the camshaft 18.

FIG. 2 shows a lifting curve 23 which can be used, on the one hand, forconventional valve opening via the rocker arm roller 17 and, on theother hand, for opening the exhaust valve via the finger 20 during aninduction stroke of the four-stroke engine, for example to createso-called internal exhaust gas recirculation in the engine (IEGR).

The curve portion 23 a here illustrates the main lifting motion of thevalve of about 12 millimeters, when the cam ridge 22 passes the rockerarm roller 17. When the cam ridge 22 then acts upon the activated finger20, the lift of about 1.5 millimeters occurs, as illustrated by thecurve portion 23 b.

The curve portion 23 c shows a further valve lift which can occur whenthe IEGR main function is not active. To this end, the camshaft 18 isprovided with an extra lobe (not shown in FIG. 1), within a crankshaftangular range of about 360-480 degrees, expediently at about 395-455degrees.

The height measurement of this lobe maximally remains short of themeasurement for normal exhaust valve clearance. When driving at highload and accompanying high heat generation in the engine, thermalexpansion occurs in the valve mechanism, which means that the extra lobecan act upon the rocker arm roller 17 so that the exhaust valves aregiven a small lift, in the order of magnitude of about 0.5 millimeters.As an alternative to the valve mechanism which is described above, avalve mechanism described in WO 03/031778 can be used. The main camcurve is here provided with lobes for normal valve lift andtemperature-dependent IEGR, while an extra cam curve is provided with alobe for activable IEGR.

The invention should not be considered limited to the illustrativeembodiments described above, but rather a host of further variants andmodifications are conceivable within the scope of the following patentclaims.

1. An apparatus for achieving internal EGR in a four-stroke internalcombustion engine, comprising, for each cylinder and piston associatedwith the cylinder: at least one inlet valve and at least one exhaustvalve for controlling connection between a combustion chamber in thecylinder and an inlet system and exhaust system respectively; a rotarycamshaft with a cam curve designed to interact with a follower member,the cam curve having a first lobe portion for generating a normalexhaust valve lift of the engine and a second lobe portion having aheight measurement over and above a basic curve of the camshaft, theheight measurement for the second lobe portion falling short of a heightmeasurement for normal exhaust valve clearance when driving at a firstload and heat development in the engine, and which height measurementfor the second lobe portion, as a result of thermal expansion in thevalve mechanism, exceeds the measurement for normal exhaust valveclearance when driving at a second load and heat development in theengine, the second load and heat development being higher than the firstload and heat development, wherein the second lobe portion is situatedwithin a crankshaft angular range of about 360-480 degrees.
 2. Theapparatus as claimed in claim 1, wherein the second lobe portion issituated within a crankshaft angular range of about 395-455 degrees. 3.The apparatus as claimed in claim 1, wherein a second follower member isswitchable between an inactive and an active position for provision ofinternal EGR independent of engine load and heat conditions.
 4. Theapparatus as claimed in claim 2, wherein a second follower member isswitchable between an inactive and an active position for provision ofinternal EGR independent of engine load and heat conditions.